The present invention relates to electrical safety, and more particularly to monitoring of AC voltages using voltage indicators. A voltage indicator is generally a low cost device that pre-verifies electrical isolation before maintenance personnel open a control panel and risk exposure to hazardous voltages. Typically mounted to the panel exterior and hardwired into the load side of the main disconnect, this device provides electrical maintenance with an additional safety value. Easy to apply, low cost, quick installation, and inherent reliability makes a voltage indicator a very effective electrical safety device.
Creating and insuring an electrically safe work condition is critical for electricians performing maintenance on de-energized systems. The presence of voltage is the only determining factor if an electrical accident or an arc flash can possibly occur—No voltage, No accident, No arc flash. “Voltage or no voltage” is also the basis of the NFPA 70E's (National Fire Protection Association Standard's for Electrical Safety Requirements for Employee Workplaces) two primary themes: a) establishing an electrically safe work condition, and b) achieving safety while working on energized systems. A voltage warning indicator is like a ‘hard wired voltmeter’ with the advantage that it needs no power supply or batteries because it is powered from the same ‘voltage’ that it indicates. A voltage indicator is an additional safety measure between maintenance personnel and hazardous voltage.
U.S. Pat. No. 6,703,938 to Clarke, herein incorporated by reference in its entirety, illustrates one type of electrical safety monitor. Despite the advances of Clarke and other prior art devices, problems remain. The inventor has recognized a problem not addressed by Clarke or other devices in the industry. In particular, there is not a means to reliably provide a zero “OFF” energy state indication. Electricians verify proper operation of their voltmeters with the “Live-Dead-Live” procedure. The first step of this procedure validates the voltmeter to a known voltage (Live) source. Once validated, the electrician uses the voltmeter to verify the electrical system is de-energized (Dead). Lastly, the voltmeter needs to be validated again to a known (Live) source to insure the voltmeter is still fully functional. The design of Clark transitions well from a live state to a dead state. However, once it is in the dead state it cannot provide a positive indication of zero energy. In other words, if the user disconnects the power from the electrical system, one cannot discern between failure and an off state of the voltage indicator. A test feature on the voltage indicator allows the electrician a means to inject a test current into the circuit, which temporarily re-energizes the circuit to insure it is still fully functional. This feature allows the device to transition from dead to live thereby meeting the requirements of the “Live-Dead-Live” procedure.